Sonochemical process for the preparation of alpha-CuSe nanocrystals and flakes

alpha-CuSe crystals of different sizes and shapes have been synthesized by a sonochemical method using the less hazardous elemental Se and Cu(Ac)(2) as precursors under an atmosphere of H-2/Ar (5 : 95 v/v). X-ray diffraction (XRD), energy-dispersive analytical X-ray (EDAX) and inductively coupled plasma (ICP) have been applied to characterize the products. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) results show that they are crystallized nanoparticles of tens of nanometers or flakes of 1 mm, depending on the irradiation time. Thermogravimetric analysis (TGA) indicates that the products are stable up to about 480 degreesC. Diffusion reflection spectra (DRS) reveal that both of them show an indirect band gap with a similar value of about 1.31 eV. Photoacoustic spectra results show that the nanoparticles and the flakes have direct band gaps of about 2.39 eV and 2.21 eV, respectively. This is the first report of the optical properties of alpha-CuSe. We propose an in situ reduction/reaction mechanism to explain the formation of CuSe. The influence of ultrasound on the shape and the size of the product is discussed. The chelating role of the DMSO solvent in the reaction has also been studied.